Recently, fuel cells, in particular polymer electrolyte fuel cells, have been receiving attention as clean and energy-efficient fuels for various applications, for example, in powering the electric cars. The fuel cell is, in essence, a generator which electrochemically produces electricity upon receipt of fuel gas (hydrogen) and oxidant gas (air). The polymer electrolyte fuel cell is provided in its inside with an electrolyte membrane composed of proton conductive solid polymers, which electrolyte membrane works well in humidified conditions. In a polymer electrolyte fuel cell system is thus provided a humidifier for humidifying a dry oxidant gas to be supplied to a fuel cell stack (for example, see Patent document 1).
The aforementioned fuel cell stack is a power-generating component with a plurality of single cells stacked on top of each other in layers, and each single cell is comprised of a solid polymer membrane sandwiched between separators; the number and size of the single cells may be determined according to the voltage or power required for an intended application such as a fuel cell automotive vehicle.
The aforementioned humidifier, for example, is constructed with a moisture vapor-exchangeable hollow fiber membrane provided therein, and an oxidant gas discharged from the fuel cell stack (hereinafter referred to as “exhaust gas”) is passed outside the hollow fiber membrane and inside the humidifier while a newly supplied oxidant gas is passed inside the hollow fiber membrane so that moisture vapors contained in the exhaust gas are transferred into the newly supplied oxidant gas.
Patent Document 1: JP 2002-75418 A (Paragraph 0016, FIGS. 1 and 3)